(1) Field of the Invention
The present invention relates to a method of activating an electric motor in a hybrid power plant of a multi-engined aircraft, and to an aircraft applying the method.
(2) Description of Related Art
An aircraft may have a hybrid power plant with a plurality of engines/motors. In particular, a rotorcraft is provided with at least one engine for driving at least one rotor in rotation via at least one main power transmission gearbox.
A power plant may possess at least two fuel-burning engines, for example. In addition, the power plant may optionally be fitted with at least one electric motor suitable for delivering additional power.
Such a power plant is thus referred to as a “hybrid” power plant because of the presence of engines and an electric motor.
The use of an electric motor on a vehicle, and in particular an aircraft, raises difficulties. Electrical energy can only be stored in batteries, however batteries present harmful weight.
Under such circumstances, the extra power delivered by an electric motor can be affected by the presence of heavy batteries required to power such an electric motor.
Document FR 2 998 542 describes a rotary wing aircraft having three motors/engines, and a method of controlling the aircraft.
In particular, the aircraft has two main engines and a main regulator system regulating the main engines in application of a variable speed setpoint. The aircraft also includes a secondary motor, and a secondary regulator system regulating the secondary motor in application of a constant setpoint. The secondary regulator system is independent of the main regulator system.
The two main engines are fuel-burning engines, and the secondary motor may be an electric motor.
The secondary motor may be started or used continuously during a flight, or it may be used intermittently in application of alternative procedures. In particular, the secondary motor is inhibited in flight while the aircraft is flying at a speed of advance that is greater than a speed threshold.
Document FR 2 962 404 describes an architecture for a rotary wing aircraft with a hybrid power plant. That architecture has fuel-burning engines connected to a main power transmission gearbox. That architecture also includes an electrical machine that is likewise mechanically engaged with the main gearbox.
Document WO 2014/009620 describes an architecture having two main engines. That architecture also includes an auxiliary engine connected to the two main engines.
Document U.S. Pat. No. 8,727,271 describes an aircraft having a turboshaft engine. The turboshaft engine is connected to an electricity generator. The electricity generator then powers an electric motor suitable for rotating a rotor or a propeller.
Furthermore, the aircraft has batteries suitable for powering the electric motor.
Document EP 2 148 066 describes a power plant having an electric motor for starting a turboshaft engine. The electric motor can operate in flight in generator mode to generate electricity, or in motor mode in order to contribute to driving a main power transmission gearbox.
Document FR 2 978 124 describes a method of controlling a group of engines developing power required to drive a rotor. The group of engines has at least one electrical member, electricity storage means, and a first number of fuel-burning engines greater than or equal to two. A processor unit executes instructions for evaluating a main condition whereby the group of engines can develop the required power while resting one of the fuel-burning engines, and where appropriate for resting one engine and accelerating a second number of non-resting engines, and for making the electrical member operate in motor mode, if necessary, the electrical member operating temporarily in electricity generator mode when the storage means is discharged.
Document FR 2 997 382 describes a method of managing an engine failure on a rotary wing aircraft having a hybrid power plant with at least two fuel-burning engines, at least one electrical machine, and a main power transmission gearbox. In that method, the operation of the engines is monitored during each flight in order to detect a failure of any one of them.
Document US 2014/0034781 is also known.